Ústav strojírenské technologie

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Structural Phenomena Introduced by Rotary Swaging: A Review
(MDPI, 2024-01-18) Kunčická, Lenka
Rotary swaging is an industrially applicable intensive plastic deformation method. Due to its versatility, it is popular, especially in the automotive industry. Similar to the well-known methods of severe plastic deformation (SPD), rotary swaging imparts high shear strain into the swaged materials and thus introduces grain refinement down to a very fine, even ultra-fine, level. However, contrary to SPD methods, one of the primary characteristics of which is that they retain the shapes and dimensions of the processed sample, rotary swaging enables the imparting of required shapes and dimensions of workpieces (besides introducing structure refinement and the consequent enhancement of properties and performance). Therefore, under optimized conditions, swaging can be used to process workpieces of virtually any metallic material with theoretically any required dimensions. The main aim of this review is to present the principle of the rotary swaging method and its undeniable advantages. The focus is primarily on assessing its pros and cons by evaluating the imparted microstructures.
The effect of strain rate and anisotropy on the formability and mechanical behaviour of aluminium alloy 2024-T3
(MDPI, 2024-01-13) Harant, Martin; Verleysen, Patricia; Forejt, Milan; Kolomý, Štěpán
The present study focuses on the mechanical behaviour and formability of the aluminium alloy 2024-T3 in sheet form with a thickness of 0.8 mm. For this purpose, tensile tests at quasi-static and intermediate strain rates were performed using a universal testing machine, and high strain rate experiments were performed using a split Hopkinson tension bar (SHTB) facility. The material’s anisotropy was investigated by considering seven different specimen orientations relative to the rolling direction. Digital image correlation (DIC) was used to measure specimen deformation. Based on the true stress–strain curves, the alloy exhibited negative strain rate sensitivity (NSRS). Dynamic strain aging (DSA) was investigated as a possible cause. However, neither the strain distribution nor the stress–strain curves gave further indications of the occurrence of DSA. A higher deformation capacity was observed in the high strain rate experiments. The alloy displayed anisotropic mechanical properties. Values of the Lankford coefficient lower than 1, more specifically, varying between 0.45 and 0.87 depending on specimen orientations and strain rate, were found. The hardening exponent was not significantly dependent on specimen orientation and only moderately affected by strain rate. An average value of 0.183 was observed for specimens tested at a quasi-static strain rate. Scanning electron microscopy (SEM) revealed a typical ductile fracture morphology with fine dimples. Dimple sizes were hardly affected by specimen orientation and strain rate.
Mechanisms of plastic deformation and fracture in coarse grained Fe-10Al-4Cr-4Y2O3 ODS nanocomposite at 20-1300°C
(Elsevier, 2023-05-01) Gamanov, Štěpán; Luptáková, Natália; Bořil, Petr; Jarý, Milan; Mašek, Bohuslav; Dymáček, Petr; Svoboda, Jiří
The coarse-grained Fe-10Al-4Cr-4Y2O3ODS nanocomposite (denoted as FeAlOY) has been developed by the authors and shows promising potential for high-temperature structural applications at 1000-1300 & DEG;C. Compared to classical ODS alloys, the FeAlOY contains ten times higher volume fraction of the stable Y2O3 nanodispersion, which gives the alloy its high-temperature strength. Furthermore, the high content of Al in the matrix guarantees excellent oxidation resistance. In practice, one can expect that the FeAlOY is loaded in the temperature range of 20-1300 & DEG;C due to intermittent device operation. To ensure a safe operation, it is necessary to determine the tensile strength and ductility of the FeAlOY in the whole temperature range and detect the dominant mechanisms of strengthening, plastic deformation, and fracture in the characteristic temperature ranges. Above 1100 & DEG;C the FeAlOY reaches ultimate tensile strength of 100 MPa and plasticity of 1%. However, in the temperature range of 400-600 & DEG;C, the plasticity can climb above 40%. The achieved results can also be utilized for the design of the FeAlOY pieces shaping by hot pressing. & COPY; 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
The Influence of Foundry Scrap Returns on Chemical Composition and Microstructure Development of AlSi9Cu3 Alloy
(MDPI, 2023-05-03) Šmalc, Jan; Vončina, Maja; Mrvar, Primož; Balaško, Tilen; Krutiš, Vladimír; Petrič, Mitja
Recycling is now, more than ever, an important part of any foundry process due to the high cost of energy. The basis of the work presented here is a study of the addition of foundry scrap returns to the melt in order to reduce material and energy costs. The most important issue in such a process is the quality of both the prepared melt and final product. In this work, scrap returns were added to the AlSi9Cu3 base alloy in different proportions. Chemical composition was monitored, the solidification path was predicted by CALPHAD calculations and monitored by thermal analysis, and the formed microstructure was studied. The mechanical properties were also determined. The results showed that as the amount of scrap returns increased, elements such as Fe, Ni, Pb, Sr, etc. were more built up and elements such as Mg, Mn, Cr, etc. were decreased due to oxidation. The different chemical composition led to a reduced Mn:Fe ratio, resulting in the formation of needle-like Fe-rich phases and a decrease in mechanical properties.
Change in Dimensions and Surface Roughness of 42CrMo4 Steel after Nitridation in Plasma and Gas
(MDPI, 2022-10-06) Dobrocký, David; Pokorný, Zdeněk; Joska, Zdeněk; Sedlák, Josef; Zouhar, Jan; Majerík, Jozef; Studený, Zbyněk; Procházka, Jiří; Barényi, Igor
The influence of plasma nitriding and gas nitriding processes on the change of surface roughness and dimensional accuracy of 42CrMo4 steel was investigated in this paper. Both processes almost always led to changes in the surface texture. After plasma nitriding, clusters of nitride ions were formed on the surface of steel, while gas nitriding very often led to the new creation of a formation of a “plate-like” surface texture. In both cases of these processes, a compound layer in specific thickness was formed, although the parameters of the processes were chosen with the aim of suppressing it. After the optimizing of nitriding parameters during nitriding processes, it was found that there were no changes in the surface roughness evaluated using the Ra parameter. However, it turned out that when using a multi-parameter evaluation of roughness (the parameters Rz, Rsk and Rku were used), there were presented some changes in roughness due to nitriding processes, which affect the functional behavior of the components. Roughness changes were also detected by evaluating surface roughness profiles, where nitriding led to changes in peak heights and valley depths. Nitriding processes further led to changes in dimensions in the form of an increase of 0.032 mm on average. However, the magnitude of the change has some context on chemical composition of material. A larger increase in dimensions was found with gas nitriding. The change in the degree of IT accuracy is closely related to the change in dimension. For both processes, there was a change of one degree of IT accuracy compared to the ground part (from IT8 to IT9). On the basis of the achieved dimensional accuracy results, a coefficient of change in the degree of accuracy IT was created, which can be used to predict changes in the dimensional accuracy of ground surfaces after nitriding processes in degrees of accuracy IT3–IT10. In this study, a tool for predicting changes in degrees of accuracy of ground parts after nitriding processes is presented.

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